Dehydrogenation process

ABSTRACT

Process for the catalytic dehydrogenation of ethylbenzene in which a feedstock containing ethylbenzene and steam is supplied into the inlet of a tubular reactor containing a dehydrogehation catalyst. Within the reactor, the feedstock flows through at least a portion of the reactor along a spiral flow path extending longitudinally of the reactor. The resulting styrene product is then recovered from a downstream or outlet section of the reactor. The spiral flow path through which the feedstock is passed is located at least adjacent the inlet side of the reactor and at least a portion of the spiral flow path contains a particulate dehydrogenation catalyst. The spiral flow path may extend throughout a major portion of the elongated tubular reactor and may contain a particulate dehydrogenation catalyst in a substantial portion there.

BACKGROUND OF THE INVENTION

The catalytic dehydrogenation of ethylbenzene to produce styrene istypically carried out at temperatures within the range of about 540-660°C. under near atmospheric or even subatmospheric pressure conditions.Typically, an ethylbenzene steam feed having a steam to ethylbenzenemole ratio of perhaps 7 or 8 or even higher is passed over adehydrogenation catalyst such as iron oxide in an adiabaticdehydrogenation reactor. The dehydrogenation reactor may be of variousconfigurations including a radial flow reactor such as disclosed in U.S.Pat. No. 5,358,698 to Butler et al or a linear or tubular reactor suchas disclosed in U.S. Pat. Nos. 4,287,375 and 4,549,032, both to Moelleret al. As disclosed, for example in the aforementioned '032 patent toMoeller et al, an iron-oxide-based dehydrogenation catalyst is employedin a tubular reactor containing a plurality of reaction tubes which areheated by a hot molten salt bath.

Yet another reactor system for the catalytic dehydrogenation ofethylbenzene to produce styrene is disclosed in U.S. Pat. No. 6,096,937to Butler et al. In the Butler et al system, a reactor system comprisesa furnace structure which incorporates a plurality of internal reactortubes which contain a dehydrogenation catalyst and which operate in anascending heat mode. Here, the reactor system incorporates gas-firedheaters which heat the interior of the furnace to a temperature suitablefor dehydrogenation to bring the temperature within the reactor tubes tothe desired level by the application of heat which varies along thelength of the tubes.

SUMMARY OF THE INVENTION

In accordance with the present invention, there is provided a processfor the catalytic dehydrogenation of ethylbenzene in a tubular reactor.In carrying out the invention, a feedstock containing ethylbenzene andsteam is supplied into the inlet of a tubular reactor containing adehydrogenation catalyst. The tubular reactor is operated undertemperature conditions effective to cause the dehydrogenation ofethylbenzene with the attendant production of styrene in the presence ofthe dehydrogenation catalyst. Within the reactor, the feedstock flowsthrough at least a portion of the reactor along a spiral flow pathextending longitudinally of the reactor. The resulting styrene productis then recovered from a downstream or outlet section of the reactor.Preferably, the spiral flow path through which the feedstock is passedis located at least adjacent the inlet side of the reactor, and at leasta portion of the spiral flow path contains a particulate dehydrogenationcatalyst. In a further embodiment of the invention, a spiral flow pathextends throughout a major portion of the elongated tubular reactor andat least a substantial portion of the spiral flow path contains aparticulate dehydrogenation catalyst. Preferably, the steam to styrenemole ratio of the feedstock is about 6 or less and more preferablywithin the range of about 5-6. The invention is particularly applicableto a variable heat (non-adiabatic) process in which heat is appliedexternally to the tubular reactor to provide an amount of heat whichvaries along the length of the tubular reactor.

In a further aspect of the invention, a feedstock containingethylbenzene and steam is supplied into a plurality of tubular reactorslocated within the interior of a dehydrogenation reactor vessel. Thetubular reactors are arranged in a parallel relationship relative to oneanother in which the tubular reactors are spaced laterally from oneanother and are spaced from the interior wall of the reaction vessel.The tubular reactors each have a mixing stage comprising alongitudinally-extending helical baffle providing a spiral flow path formixing of the ethylbenzene and steam within the reactor. The interior ofthe reaction vessel is heated by a gas-fired or other suitable heatingsystems in order to provide a heating zone externally of the tubularreactor to provide an amount of heat which varies along the lengths ofthe tubular reactors. The supplied mixture of ethylbenzene and steamflows through the parallel tubular reactors into contact with aparticulate dehydrogenation catalyst in the reactor under temperatureconditions, resulting from the externally-applied heat, which areeffective to cause the dehydrogenation of ethylbenzene to styrene in thepresence of the dehydrogenation catalyst. Subsequent to thedehydrogenation reaction, the styrene product is recovered from thetubular reactors through outlets located downstream of thedehydrogenation catalyst.

In a further aspect of the invention, there is provided a reactionsystem for the catalytic reaction of a plurality of reactants in a feedstream. The reaction system comprises a plurality of parallel,elongated, tubular reactors having inlet and outlet sides. An inletmanifold is connected to the tubular reactors in order to supply amixture of reactants to the inlet sides of the tubular reactors. Thereactors incorporate a mixing section adjacent the inlet sides thereof,each reactor comprising at least one static baffle in an elongatedhelical configuration comprising a spiral flow path. A reaction sectionin each of the tubular reactors is located downstream of the initialmixing section and comprises a bed of catalyst particles. An outletmanifold is connected to the outlet side of the tubular reactors and iseffective to supply reaction product from the tubular reactors to asuitable recovery system.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of a reactor incorporating aplurality of tubular reactors for use in carrying out the presentinvention.

FIG. 2 is a perspective view with parts broken away of a static mixtureincorporating a helical baffle providing a spiral flow path for themixing of benzene and steam.

FIG. 3 is a perspective view of a modified form of a static mixtureincorporating two flights of helical baffles.

FIG. 4 is a schematic illustration of one form of tubular reactorconfigured with an initial spiral mixing section.

FIG. 5 is a schematic illustration of another embodiment of theinvention incorporating several spaced mixing stages.

FIG. 6 is a schematic illustration of yet another embodiment of theinvention incorporating helical baffles extending throughout asubstantial length of tubular reactor.

FIG. 7 is a graphical presentation showing the relationship betweenstyrene selectivity and ethylbenzene conversion for a procedureincorporating the present invention in comparison with a relativelylinear mixing system.

FIG. 8 is a graphical representation showing the relationship betweenstyrene selectivity and the steam to hydrocarbon ratio for the twosystems depicted in FIG. 7.

FIG. 9 is a graphical representation showing the relationship betweenethylbenzene conversion and reaction temperature for the two modes ofoperation depicted in FIGS. 7 and 8.

DETAILED DESCRIPTION OF THE INVENTION

The present invention may be carried out employing tubular reactors ofany suitable configuration. Thus, a tubular reactor of the typedisclosed in the aforementioned patent to Moeller et al may be employed.Preferably, however, the invention will be carried out employing tubularreactors employed within a electrically-heated or gas-fired furnaceoperated in a variable heat mode such as disclosed in U.S. Pat. No.6,096,937 to Butler et al, and the invention will be described withreference to this reactor configuration. Thus, the reactor may beoperated as an ascending heat reactor, as disclosed in theaforementioned '937 patent to Butler et al, or it may be operated as arelatively constant heat adiabatic reactor. Regardless of the nature ofthe operation of the system, the reactor tubes will incorporate ahelical spiral flow mixing section as described in greater detail below.

Referring initially to FIG. 1, there is shown a schematic illustrationof an ascending-heat ethylbenzene reactor which is disclosed as having areaction chamber defined by an external shell 11 and having an inletmanifold 12 and an outlet manifold 13. A supply line 14 is connected toinlet manifold 12 to supply an ethylbenzene-steam feed stock, and aproduct flow line 15 containing styrene and unreacted ethylbenzene andsteam is connected to the outlet manifold 13.

The central section of the ethylbenzene reactor includes a furnace 11inside which is located a series of reactor flow tubes 16 which areconnected in parallel to the inlet manifold 12. The open bore of eachtube 16 is exposed to the inlet manifold 12 to allow the ethylbenzenesteam feed to enter through line 14 into inlet manifold 12 and totraverse tubes 16 into outlet manifold 13. Although, only three reactortubes are disclosed in this schematic drawing, in actual practice alarge multitude of such tubes normally would be provided in the reactor.A plurality of burners 18 are located at the top of the furnace shell.Burner tubes 18 are connected to a source of fuel such a natural gas,hydrogen, or other combustible gas which is provided by means of fuelinlet line 17 communicating with heater elements 18. A combustionproducts exhaust line 19 communicates through the wall of chamber 11 tocarry the products of combustion from the flames of nozzles 24 of theheater elements. A source of oxygen may also be provided by means of aseparate oxygen supply line or air supply line which may be connected toburner tubes 18 separately or may be passed through a mixer box prior toentering line 17 where air or oxygen can be mixed with the gaseous fuel.

In typical operation, an ethylbenzene feedstock (a mixture ofethylbenzene and steam) is provided through inlet line 14 and flows intothe reactor tubes 16. The interiors of reactor tubes 16 may becompletely or partially filled with a suitable EB dehydrogenationcatalyst. Those skilled in the art are aware of suitable dehydrogenationcatalysts which can be advantageously utilized in the present invention.The ethylbenzene feedstock flows from inlet header 12 through tubes 16and across the chosen catalyst where it undergoes dehydrogenation toproduce the resulting styrene product.

Concurrently with supply of the ethylbenzene feedstock, the gaseousmixture of fuel and oxygen source flows through line 17 and into heaternozzles 24. An ignition source is provided upon startup of the reactorand the gas is continuously passed through nozzles 24 and burns as itexits the nozzles. A minor amount of experimentation can determine theparticular nozzle sizes to use for obtaining an ascending-heat thermalreactor. Thus, as ethylbenzene enters line 14 and passes through chamberinlet header 12 into reactor tubes 16, it is passed across thedehydrogenation catalyst contained in the reactor tubes 16 and subjectedto an increasing level of heat input due to the gaseous fuel beingconsumed. Although gaseous fuel is desirable, it is, of course, possibleto use a liquid fuel, which can be atomized by the oxygen source gas ata point prior to entering line 17. Other conventional nozzle-heaterarrangements can be used with different fuel sources. In addition, it ispossible that, rather than a chemically-driven heat supply, one couldsubstitute electrical heating elements which vary in heat generationfrom the input end of the reactor to the output end of the reactor, toobtain the increasing heat supply for the reactor. Thus, one skilled inthe art could substitute electrical heating elements for gas-firedheaters 18 with increasing heat output towards the end of the heatingelements associated with the output end of the reactor tube 16.

Usually, it will be desirable to use a heat source that is compatiblewith the refining operations around the dehydrogenation reactor wherethe most available fuel is usually hydrogen or a compressed natural gasand therefore the description here is defined in terms of a gas-firedheating system. Upon traversing the length of reactor tubes 16 acrossthe catalyst contained therein, a substantial dehydrogenation of theethylbenzene feed is accomplished, and the product exiting into theoutlet header contains substantial styrene, which is then passed throughproduct flow line 15 to a heat exchanger 28 in indirect heat exchangewith the feed stock in inlet line 14. From the heat exchanger, thedehydrogenation product is passed to a system (not shown) for furtherpurification and removal of non-styrene products such as ethylbenzene,benzene, toluene, and hydrogen. As previously mentioned, the combustiongases exiting nozzle 24 flow out through gas exhaust conduit 19 in thebottom of the heater box. Thus is described a reactor fordehydrogenating ethylbenzene into styrene which is defined as anascending-heat reactor to provide heat input for the endothermicethylbenzene dehydrogenation reaction and, furthermore, to provideincreasing amounts of heat toward the end of the dehydrogenationreaction as the components being reacted are being used up and thereaction equilibrium tends to shift to the left.

As described in the aforementioned Butler et al patent, various changescan be made in the described dehydrogenation reactor system. The flowrate in terms of the liquid hourly space velocity (LHSV) through thetubes can be changed by varying the diameter of the reactor tubes alongtheir length. For example, the reactor tubes can be smaller at the inletend and larger at the outlet end to provide a decreasing LHSV down thelength of each reactor tube. For a further description of a suitablereactor system for the dehydrogenation of ethylbenzene employing anascending heat mode of operation, reference is made to theaforementioned U.S. Pat. No. 6,096,937 to Butler et al, the entiredisclosure of which is incorporated herein by reference.

It is to be recognized that the parallel reactor tube configuration ofthe type disclosed in the Butler et al '937 patent can be employed inadiabatic reaction systems of the type more conventionally used in thedehydrogenation of ethylbenzene to produce styrene. In any case, it willbe advantageous in carrying out the invention to employ a plurality ofparallel tubular reactors with appropriate manifolding at the inlet andoutlet sides of the reactors as described, for example, in the '937patent.

Turning now to FIG. 2, there is illustrated a preferred form of a staticinline mixer which can be employed in carrying out the invention. FIG. 2is a perspective view of a cylindrical static mixer employing a helicalbaffle to provide a spiral flow path along the length of the mixer. InFIG. 2, the mixer is shown with one-half of the outer cylindrical shellbroken away to reveal the interior of the static mixture. As shown inFIG. 2, the mixer incorporates a cylindrical shell 30 with an internalhelical baffle 32 providing a spiral flow path for the feedstock mixtureas indicated by arrows 34. In the embodiment illustrated in FIG. 2, thebaffle has a pitch of about 30° (from the longitudinal axis at themixer) to provide for good mixing of the steam and ethylbenzenecomponents and to provide for a relatively constant radial temperaturegradient. That is, the temperature is relatively constant across thewidth of the mixer.

While only a single or continuous helical baffle is employed in themixer of FIG. 2, a further embodiment of the invention involves the useof an inline mixer having a plurality of helical baffle sections. Astatic mixer incorporating this embodiment of the invention isillustrated in FIG. 3, which is a perspective illustration, with partsbroken away of a mixer having a first baffle section 36 and at least onesecond baffle section 38, which is angularly displaced (e.g., by 90° inthe embodiment shown), with respect to the first baffle section 36, of adifferent pitch than the first baffle. This embodiment of the inventionis particularly useful where the mixture is incorporated in only aportion of the tubular reactor as described below and provides forthorough and efficient mixing of the two components, initially afterwhich a generally more linear flow takes place throughout the remainderof the tubular reactor. As an example of the embodiment illustrated inFIG. 3, baffle section 38 may be followed by baffle section 36 a(displaced by 90°) followed in turn by baffle section 38 a againdisplaced by 90°. In a further embodiment of the invention (not shown)one baffle may have a designated pitch with the other baffle having adifferent pitch.

FIG. 4 is a schematic illustration with parts broken away of a tubularreactor configured with an initial helical flow mixing section with theremainder of the reactor packed with particulate dehydrogenationcatalysts. While only a single tubular reactor is illustrated in FIG. 4and in the following FIGS. 5 and 6, it is to be understood that acommercial dehydrogenation reactor will have a plurality of tubularreactors which are manifolded as described above with respect to theaforementioned '937 patent. For example, a commercial reactorimplementing the present invention typically will contain from 500 to1500 tubular reactors connected in parallel to suitable intake andexhaust manifolding systems. More particularly, and referring to FIG. 4,the tubular reactor contains an initial static mixing section 42 whichconforms to the single baffle mixer illustrated in FIG. 2. In addition,the tubular reactor includes perforated grid plates 44, 45, 46, and 47which support a particulate dehydrogenation catalyst 48 throughout thelength of the tubular reactor and extending partially into the staticmixture. Dehydrogenation catalyst 48 may be of any suitable type,typically constituting an iron oxide-based catalyst comprising ironoxide or a mixture of iron oxide with chromium oxide and sodium oxide,as disclosed in the aforementioned U.S. Pat. No. 4,549,032 to Moeller.As illustrated, the top portion of the reactor involving most of thelength of the static mixture is free of catalysts in order to allow aspiral flow path of the reactants initially before contacting thedehydrogenation catalysts. However, the dehydrogenation catalyst mayextend further upwardly and be packed in most or even all of the initialstatic mixture.

FIG. 5 illustrates another embodiment of the invention in which atubular reactor 50 incorporates two spaced mixing stages, an initialmixing stage 52 and a second spaced and intermediate mixing stage 54.Catalyst particles 55 are interposed on suitable grid plates 56 and 57above and below the intermediate mixing section 54. Sections 52 and 54may be identical and different and may be single baffle static mixers asdisclosed in FIG. 2 or multi-baffle mixers of the type described abovewith respect to FIG. 3. As before, the catalyst particles extendupwardly into a lower portion of the baffle mixing section 52.Similarly, the catalyst particles supported on grid 57 extend upwardly,partially into the mixing section 54 to encompass at least a lowerportion of this mixing section. Alternatively, the particulatedehydrogenation catalyst may extend throughout the lengths of one orboth of mixing sections 52 and 54.

FIG. 6 illustrates yet another embodiment of the invention in which allor at least a predominant portion of the longitudinal dimension of thetubular reactor incorporates one or more helical baffles providing oneor more spiral flow paths throughout the length of the tubular reactor.In this embodiment of the invention, a tubular reactor 60 incorporates aseries of static mixers 62, 63, 65, and 66, each corresponding to amixer of the type illustrated in FIG. 2, disposed along the length ofthe tubular reactor. Each of the mixing sections is packed with aparticulate dehydrogenation catalyst 70 with the initial mixerpreferably containing catalysts in only a lower portion of the mixingsection 62, similarly, as described above with respect to FIG. 4.Alternatively, the catalyst can extend upwardly through most or all ofthe initial static mixer or even into the plenum area 72 above the mixer62. In FIG. 6, a spiral flow path is provided throughout substantiallythe length of the tubular reactor. While in the embodiment illustratedthis is provided by a plurality of mixing sections stacked one on top ofthe other, it will be recognized that a continuous helical baffle can beprovided by a single helix extending throughout the length of thetubular reactor.

The present invention, through the use of an inline static mixingsection encompassing all or a portion of the tubular reactor, offerssignificant advantages in terms of selectivity to styrene production andin terms of the possibility of relatively low steam to hydrocarbon moleratio (SHR).

In experimental work respecting the present invention, tests werecarried out in an 8-inch diameter tubular reactor having an overalllength of about 14 feet and a total catalyst length of 10 feet. Thetests were carried out employing equal amounts of an iron oxide-baseddehydrogenation catalyst using two types of static mixing schemes. Inone set of tests, linear flow mixing was synthesized through the use ofspaced beds of chrome molybdenum steel cylindrical particles, and in theother set of tests simulating the present invention, spiral flow staticmixtures of the type illustrated in FIG. 2 were employed. In the firstset of tests, the iron oxide-based catalyst in the form of 5.5millimeter diameter cylinders of about 8 mm in length were loaded intothe 8-inch diameter tube with 6 mixers of chrome molybdenum steelcylindrical particles interposed between the successive beds ofcatalysts. The mixers of chrome molybdenum steel cylindrical particleswere formed by 3-inch thick beds formed of 1-inch diameter by 1-inchlong chrome-moly cylindrical particles. Thus, in this set ofexperimental work the catalyst particles were loaded into the reactor toprovide a column of catalyst particles of about 1-½ feet followed by 3inches of the chrome-moly particles followed again by about 1-½ feet ofcatalyst particles. This sequence of catalyst particles and chrome-molycylindrical particles was repeated until the sixth chrome-moly particlemixing bed was in place. Thereafter, additional catalyst was added untila total of about 3.5 cu. ft of catalysts were in place in the tubularreactor. In the second set of tests simulating the practice of thepresent invention, four 2-foot sections of static mixers incorporating ahelical baffle as depicted in FIG. 2, were loaded into the 8-inchdiameter tube. The catalyst loading was carried out by placing theinitial 2-foot section of mixer into the tube and then filling thissection with catalyst and then repeating this procedure with a second,third, and fourth placement of 2-foot sections of mixers. Additionalcatalyst was added after the final mixer was in place to bring thecatalyst bed to about 20 inches below the top of the tubular reactor andprovide an amount of catalyst equal to the amount of catalyst employedin the first set of experimental tests. The tests were carried out at alinear hourly space velocity (LHSV) of 1.4 hr.⁻¹ and an SHR ranging from4:1 molar to about 9.5:1 molar. An electrically-powered feed heater wasused to control the catalyst bed inlet temperature at the desired value.The temperature was controlled so that the outlet temperature was variedfrom values ranging from about 1100° to about 1120° F.

The results of this experimental work are shown in FIGS. 7, 8, and 9.Turning first to FIG. 7, this is a graph illustrating styreneselectivity SS in wt. % plotted on the ordinate versus ethylbenzeneconversion (EBC) in wt. % plotted on the abscissa. In FIG. 7, theresults for Protocol A (employing the static mixers corresponding tothose shown in FIG. 2) for a SHR values of 8 and 10 are indicated bycurve A-7. The test results obtained using the beds of chrome-moly tubes(Protocol B) are indicated by curve B-7 for SHR values of 8 and 10. Ascan be seen from an examination of the data set forth in FIG. 7,Protocol A, simulative of the present invention, showed a consistentincrease in styrene selectivity over ethylbenzene conversion ratesranging from about 62 to 68 wt. %. The use of the inline helical mixerin Protocol A showed a selectivity increase of about 0.7% as indicatedby line segment C-7 in FIG. 7.

FIG. 8 is a graph showing styrene selectivity (SS) in wt. % plotted onthe ordinate versus the SHR mole ratio (R) plotted on the abscissa. InFIG. 8 the selectivity observed for Protocol A is indicated by the data points and curve A-8. Similar data points for Protocol B areindicated by Δ and curve B-8. As indicated, Protocol A showed aconsistently better selectivity than Protocol B over a wide range ofsteam hydrocarbon ratios. More importantly, the selectivity for ProtocolA remains relatively good at SHR values down to 5:1. When the SHR isdecreased further down to 4:1 mole ratio, a substantial decrease inperformance is observed, but selectivity still remains better forProtocol A than for Protocol B. The effectiveness of Protocol A atrelatively low steam to ethylbenzene ratios within the range of about 5to 7 and especially within the range of about 5 to 6 is very significantsince it enables operation at low SHR values with substantial decreasein capital and operating costs.

A further advantage of the present invention resides in the use of thestatic inline spiral mixing protocol providing somewhat lower operatingtemperatures than with the linear flow mixers. This is illustrated inFIG. 9 which is a graph of ethylbenzene conversion (EBC) in wt. %plotted on the ordinate versus the outlet temperature (T) in degreesFahrenheit plotted on the abscissa. In FIG. 9, curve A-9 illustrates theresults for Protocol A versus the results for Protocol B as indicated bycurve B-9. As can be seen from an examination of FIG. 9, Protocol Aconsistently provided for an outlet temperature which was about 10-15°cooler than Protocol B at equal ethylbenzene conversion levels.

The present invention can be employed incorporating any suitabledehydrogenation catalyst suitable for the dehydrogenation ofethylbenzene. Such catalysts normally incorporate iron oxide along withsecondary components such as chrome oxide as well as other inorganicmaterials and are typically formulated with a binder in particle sizesof about ⅛-inch. One suitable catalyst for use in carrying out thepresent invention is iron oxide catalyst promoted with potassiumcarbonate plus trace metals for selectivity enhancement available fromCriterion Catalyst Company under the designation “Flexicat Yellow.”

Having described specific embodiments of the present invention, it willbe understood that modifications thereof may be suggested to thoseskilled in the art, and it is intended to cover all such modificationsas fall within the scope of the appended claims.

What is claimed:
 1. A process for the production of styrene by thecatalytic dehydrogenation of ethylbenzene comprising: a. supplying afeedstock containing ethylbenzene and steam into a tubular reactorcontaining a dehydrogenation catalyst; b. operating said tubular reactorunder temperature conditions effective to cause the dehydrogenation ofethylbenzene to styrene in the presence of said dehydrogenationcatalyst; c. flowing said feedstock within at least a portion of saidreactor along a spiral flow path located within an extendinglongitudinally of said reactor; and d. recovering styrene product from adownstream section of said reactor.
 2. The process of claim 1 whereinsaid feedstock is passed along said spiral flow path at a locationadjacent the inlet side of said reactor.
 3. The process of claim 1wherein at least a portion of said spiral flow path contains aparticulate dehydrogenation catalyst.
 4. The process of claim 1 whereinthe steam to ethylbenzene mole ratio of said feedstock is about 10 orless.
 5. The process of claim 1 wherein the steam to ethylbenzene moleratio of said feedstock is within the range of 5-6.
 6. The process ofclaim 1 wherein said spiral flow path extends throughout a major portionof the length of the elongated tubular reactor and at least a portion ofsaid spiral flow path contains a particulate dehydrogenation catalyst.7. A process for the production of styrene by the catalyticdehydrogenation of ethylbenzene comprising: a. supplying a feedstockcontaining ethylbenzene and steam into a tubular reactor having a mixingsection comprising a longitudinally-extending helical baffle inside thetubular reactor providing a spiral flow path for the mixing of saidethylbenzene and steam; b. heating said tubular reactor by applying heatexternally of said tubular reactor to provide an amount of heat whichvaries along the length of the tubular reactor; c. supplying said mixedsteam and ethylbenzene into contact with a particulate dehydrogenationcatalyst in said tubular reactor under temperature conditions effectiveto cause the dehydrogenation of ethylbenzene to styrene in the presenceof said dehydrogenation catalyst; and d. recovering styrene product fromsaid reactor through an outlet downstream of said dehydrogenationcatalyst.
 8. The process of claim 7 wherein said mixing sectionincorporates a second helical baffle having a pitch different from thepitch of said first recited helical baffle.
 9. The process of claim 7wherein said feedstock is passed along said spiral flow path at alocation adjacent the inlet side of said reactor.
 10. The process ofclaim 7 wherein at least a portion of said spiral flow path contains aparticulate dehydrogenation catalyst.
 11. The process of claim 7 whereinsaid helical baffle extends throughout a major portion of the length ofthe elongated tubular reactor to provide said spiral flow path and atleast a portion of said spiral flow path contains a particulatedehydrogenation catalyst.
 12. The process of claim 7 wherein the steamto ethylbenzene mole ratio of said feedstock is about 10 or less. 13.The process of claim 7 wherein the steam to ethylbenzene mole ratio ofsaid feedstock is about 6 or less.
 14. A process for the production ofstyrene by the catalytic dehydrogenation of ethylbenzene comprising: a.supplying a feedstock containing ethylbenzene and steam into a pluralityof tubular reactors located within the interior of a dehydrogenationreactor vessel and arranged in a parallel relationship with respect toone another in which the tubular reactors are spaced from one anotherand spaced from the interior wall of the reaction vessel, each of saidtubular reactor having a mixing stage comprising alongitudinally-extending helical baffle inside said each of tubularreactors providing a spiral flow path for mixing of said ethylbenzeneand steam; b. heating the interior of said reaction vessel to provideheat externally of said tubular reactor to provide an amount of heatwhich varies along the lengths of the tubular reactors; c. within saidtubular reactors, supplying said mixed steam and ethylbenzene intocontact with a particular dehydrogenation catalyst in said tubularreactors under temperature conditions resulting from the externallyapplied heat, effective to cause the dehydrogenation of ethylbenzene tostyrene in the presence of said dehydrogenation catalyst; and d.recovering styrene product from said tubular reactors through outlets ofsaid tubular reactors.
 15. The process of claim 14 wherein the mixingstages of said tubular reactors providing said spiral flow paths arelocated at least adjacent the inlets of said tubular reactor.
 16. Theprocess of claim 14 wherein the spiral flow paths of said reactorsextend throughout major portions of the lengths of the elongated tubularreactors and at least a portion of said spiral flow paths contain aparticulate dehydrogenation catalyst.
 17. The process of claim 16wherein the steam to ethylbenzene mole ratio of said feedstock is about10 or less.
 18. The process of claim 17 wherein the steam toethylbenzene mole ratio of said feedstock is within the range of 5-6.